Milling cutter with stress reliefs

ABSTRACT

A cutting tool, such as a milling cutter, includes a tool body and a plurality of pockets for receiving cutting inserts. Each pocket includes a bottom support surface, an radial support surface, an axial support surface, a first corner relief between the bottom support surface and the radial support surface, and a first stress relief formed in the first corner relief at one end of the pocket. The first stress relief is formed at an angle with respect to a plane parallel to the radial support surface. The first stress relief reduces a tensile stress of the cutting tool during a machining operation. A second and third stress relief may be formed in the first corner relief and/or in a second corner relief.

BACKGROUND OF THE INVENTION

Cutting tools, such as milling cutters, are rotatable tools ofcylindrical, conical, shaped or disk form, having a plurality of cuttingedges. Such cutters are available in many forms, such as plaincylindrical, side milling cutters, face and end mills, formed cutters,and standard and special shaped profile cutters.

End mills employing cutting inserts mounted at the front end of the toolare known in the art. The end mills can be used in several types ofapplications depending on the configuration of the cutting insertsmounted therein. The cutting inserts may present a peripheral cuttingedge for side milling, a front cutting edge for face milling and acurved cutting edge of a so-called “ball-nose” end mill for variouscopying applications. Four flute mills are probably the most common, but2, 3 or 6 flutes are also used extensively. End mills are in much usedbecause they can execute a wide variety of milling operations, and theinitial cost of the cutter is moderate. Shapes other than cylindricalare also in common use. The shank can be parallel or tapered, and neednot necessarily be equal to the cutter teeth diameter.

Usually when an end mill is in operation, the machining force is exertedagainst one edge of the cutter. The resulting moment is resisted by thetool holder which rigidly grips the cutter shank. Ignoring the fact thatthe direction of the moment changes continually as the cutter revolves,the cutter can be considered to be stressed as a cantilever.

While the matter of stress discussed above is related to avoidingfatigue that would result in tool breakage, no less important is therequirement to minimize tool deflection, in order to improve accuracyand surface finish and to reduce vibration and noise. The bendingmoment, along with the rotation of the cutter, produces a fully reversedstress condition (alternating tensile and compressive stresses), whichis the most devastating condition for fatigue.

Accordingly, there is a need for an improved cutting tool that canovercome the limitations of the known cutting tool, and reduce oreliminate the overall stress of the cutting tool.

SUMMARY OF THE INVENTION

The inventors of the invention has solved the problem of high stressassociated with conventional cutting tools by providing a pocket featurelocated proximate the area of high stress on the radial support surfacethat greatly reduces the tensile stress, thereby improving tool safetyand lifetime of the tool.

In one aspect, a cutting tool comprises a tool body including aplurality of pockets for receiving cutting inserts, each pocketcomprising a bottom support surface, a radial support surface, a firstcorner relief between the bottom support surface and the axial supportsurface, and a first stress relief formed in the first corner relief atone end of the pocket, the first stress relief formed at an angle withrespect to a plane parallel to the axial support surface, wherein thefirst stress relief reduces a tensile stress of the cutting tool duringa machining operation.

In another aspect, a cutting tool comprises a tool body including aplurality of pockets for receiving cutting inserts, each pocketcomprising a bottom support surface, an axial support surface, a radialsupport surface, a first corner relief between the bottom supportsurface and the axial support surface, a second corner relief betweenthe bottom support surface and the radial support surface, a firststress relief formed in the first corner relief at one end of thepocket, the first stress relief formed at an angle with respect to aplane parallel to the axial support surface, and a second stress reliefformed in the second corner relief, the second stress relief formed atan angle with respect to a plane parallel to the radial support surface,wherein the first and second stress reliefs reduce a tensile stress ofthe cutting tool during a machining operation.

In yet another aspect, a cutting tool comprises a tool body including aplurality of pockets for receiving cutting inserts, each pocketcomprising a bottom support surface, an axial support surface, a radialsupport surface, a first corner relief between the bottom supportsurface and the axial support surface, a first stress relief formed inthe first corner relief at one end of the pocket, the first stressrelief formed at an angle with respect to a plane parallel to the axialsupport surface, and a third stress relief formed in the first cornerrelief at an opposite end of the pocket, the third stress relief formedat an angle with respect to the plane parallel to the axial supportsurface, wherein the first and third stress reliefs reduce a tensilestress of the cutting tool during a machining operation.

BRIEF DESCRIPTION OF THE DRAWINGS

While various embodiments of the invention are illustrated, theparticular embodiments shown should not be construed to limit theclaims. It is anticipated that various changes and modifications may bemade without departing from the scope of this invention.

FIG. 1 is an isometric view of a cutting tool according to an embodimentof the invention;

FIG. 2 is an enlarged view of the pocket of the cutting tool of FIG. 1showing first and second stress reliefs for reducing stress according toan embodiment of the invention;

FIG. 3 is cross-sectional view of the pocket taken along line 3-3 ofFIG. 2;

FIG. 4 is an enlarged view of the pocket of the cutting tool of FIG. 1showing first and third stress reliefs for reducing stress according toan another embodiment of the invention; and

FIG. 5 is cross-sectional view of the pocket taken along line 5-5 ofFIG. 4.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings, wherein like reference characters representlike elements, a cutting tool 10, generally shown in FIG. 1, includes agenerally cylindrical tool body 12 that is generally radiallysymmetrical about its central, rotational axis 14 and terminates at acutting tip 15. In the illustrated embodiment, the cutting tool 10comprises a milling cutter.

The tool body 12 preferably, but not necessarily, includes a pluralityof flutes 16 each bearing a plurality of pockets 18 therein. The pockets18 are rotationally symmetrically arranged with respect to the axis 14.At least one, but possibly more, of the cutting inserts (not shown) areconfigured and dimensioned to be received within and secured to eachpocket 18. It will be appreciated that the invention is not limited bythe number of pockets 18, and that the invention can be practiced withany desired number of pockets 18, depending on the dimensions of thetool body 12.

Referring now to FIGS. 2 and 3, each pocket 18 has a bottom supportsurface 20 that may be at an angle (not shown) with respect to the axis14. The pocket 18 also includes a radial support surface 22 and anoptional axial support surface 24 that constitute radial and axialabutment surfaces, respectively, for the side walls of the insert whenmounted in the pocket 18. A first corner relief 26 is formed between thebottom support surface 20 and the radial support surface 22. Inaddition, a second corner relief 27 is formed between the bottom supportsurface 20 and the optional axial support surface 24 if the optionalaxial support surface 24 is provided in the cutting tool 10. A threadedbore 36 extends through the center of the bottom support surface 20 andis substantially perpendicular thereto. In the assembled position of thecutting tool 10, each of the cutting inserts is retained within a pocket18 by a clamping screw (not shown) that passes through a through bore ofthe cutting insert and threadingly engages the threaded bore 36 in thepocket 18.

Referring now to FIG. 3, one aspect of the invention is that each cornerrelief 26, 27 is formed with a stress relief that reduces the tensilestress on the pocket 18, thereby increasing tool life. Specifically, afirst stress relief 28 is formed in the first corner relief 26, and asecond stress relief 29 is formed in the second corner relief 27. Thatis, the first stress relief 28 is formed between the bottom supportsurface 20 and the radial support surface 22, and the second stressrelief 29 is formed between the bottom support surface 20 and the axialsupport surface 24.

The first stress relief 28 is a rounded body intersection having asubstantially circular in cross-sectional shape and is formed at anangle 30 with respect to a plane 32 that is parallel to the radialsupport surface 22. The angle 30 can be in a range between about zero(0) degrees and about ninety (90) degrees. That is, the angle 30 isgreater than zero (0) degrees, but less than ninety (90) degrees.

As shown in FIG. 2, the first stress relief 28 is formed with a radius,R1, at the intersection with the cutting tip 15 of the tool body 12. Theradius, R1, can be in a range between about 1 mm to about 3 mm. Forexample, the radius, R1, can be about 0.047 inches (approximately 1.19mm). It will be appreciated that the invention is not limited by themagnitude of the radius, R1, of the first stress relief 28, and themagnitude of the radius, R1, of the first stress relief 28 depends onthe design of the cutting insert, and other factors. In addition, thefirst stress relief 28 is also formed with a radius, R2, at theintersection with first corner relief 26, as shown in FIG. 3. Theradius, R2, can be in a range between about 1 mm to about 20 mm.

Similarly, the second stress relief 29 is a rounded body intersectionhaving a substantially circular in cross-sectional shape and is formedat an angle 31 with respect to a plane 33 that is parallel to the axialsupport surface 24. The angle 31 can be in a range between about zero(0) degrees and about ninety (90) degrees. That is, the angle 31 isgreater than zero (0) degrees, but less than ninety (90) degrees.

Similar to the first stress relief 28, the second stress relief 29 isformed with the radius, R1, at the intersection with the outer peripheryof the tool body 12. In addition, the second stress relief 29 is formedwith a radius, R3, at the intersection with the second corner relief 27.The radius, R3, can be in a range between about 1 mm to about 20 mm. Theangle 31 of the second stress relief 29 can be the same or differentthat the angle 30 of the first stress relief 28. In addition, theradius, R3, of the second stress relief 29 can be the same or differentthan the radius, R2, of the first stress relief 28.

It has been discovered that the first stress relief 28 formed in thefirst corner relief 26, and a second stress relief 29 formed in thesecond corner relief 27 produces the unexpected result of significantlyreducing the tensile stress of the pocket 18 of the cutting tool 10,thereby extending tool life. Specifically, a finite element analysis(FEA) of the tensile stress of a conventional first row pocket of thecutting tool without the stress reliefs 28, 29 of the invention produceda maximum tensile stress of about 124,210 psi at the corner relief 26and a maximum tensile stress of about 157,990 psi at the corner relief27.

By contrast, a finite element analysis of the tensile stress of a firstrow pocket 18 of the cutting tool 10 with the stress reliefs 28, 29 ofthe invention produced a maximum tensile stress of about 81,905 psi atthe stress relief 28 and a maximum tensile stress of about 71,344 psi atthe stress relief 29. In other words, the stress reliefs 28, 29 reducedthe maximum tensile stress at the corner relief 26 by about 34% and atthe corner relief 27 by about 55%, which is a significant reduction oftensile stress.

A similar finite element analysis of the second and remaining rows ofpockets of the cutting tool produces about a 20% reduction in themaximum tensile stress of the corner relief 27 and about a 27% reductionin the maximum tensile stress of the corner relief 26 as compared to aconventional pocket without the stress reliefs 28, 29.

Referring now to FIGS. 4 and 5, the pocket 18 with stress reliefs isshown according to another embodiment of the invention. In thisembodiment, the first stress relief 28 is formed in the corner relief 26at one end of the pocket 18 between the bottom support surface 20 andthe radial support surface 22. In addition, a third stress relief 34 isformed at the opposite end of the corner relief 26 between the bottomsupport surface 20 and the radial support surface 22 at an opposite endof the pocket 18.

As mentioned above, the first stress relief 28 is a rounded bodyintersection having a substantially circular in cross-sectional shapeand is formed at the angle 30 with respect to the plane 32 that isparallel to the radial support surface 22. The angle 30 can be in arange between about zero (0) degrees and about ninety (90) degrees. Thatis, the angle 30 is greater than zero (0) degrees, but less than ninety(90) degrees. The first stress relief 28 is also formed with the radius,R2, at the intersection with the first corner relief 26.

Similarly, the third stress relief 34 is a rounded body intersectionhaving a substantially circular in cross-sectional shape and is formedat an angle 35 with respect to the plane 32 that is parallel to theradial support surface 22. The angle 35 can be in a range between aboutzero (0) degrees and about ninety (90) degrees. That is, the angle 35 isgreater than zero (0) degrees, but less than ninety (90) degrees.Similar to the first stress relief 28, the third stress relief 34 isformed with a radius, R3, at the intersection with the first cornerrelief 26. The radius, R3, can be in a range between about 1 mm to about20 mm. The angle 35 of the third stress relief 34 can be the same ordifferent that the angle 30 of the first stress relief 28. In addition,the radius, R3, of the third stress relief 34 can be the same ordifferent than the radius, R2, of the first stress relief 28.

It will be appreciated that the invention can be practiced with thefirst and third stress reliefs 28, 34 formed in the first corner relief26 and the second stress relief 29 formed in the second corner relief27, or any combination thereof

As described above, the stress reliefs 28, 29, 34 produce the unexpectedresult of greatly reducing the tensile stress of the cutting tool 10,thereby greatly increasing tool life as compared to conventional toolsthat do not include the stress reliefs of the invention.

The patents and other documents identified herein are herebyincorporated by reference herein. Other embodiments of the inventionwill be apparent to those skilled in the art from a consideration of thespecification or a practice of the invention disclosed herein. It isintended that the specification and examples are illustrative only andare not intended to be limiting on the scope of the invention. The truescope and spirit of the invention is indicated by the following claims.

What is claimed is:
 1. A cutting tool comprising: a tool body includinga plurality of pockets for receiving cutting inserts, each pocketcomprising a bottom support surface, an radial support surface, a firstcorner relief between the bottom support surface and the radial supportsurface, and a first stress relief formed in the first corner relief atone end of the pocket, the first stress relief formed at an angle withrespect to a plane parallel to the radial support surface, wherein thefirst stress relief reduces a tensile stress of the cutting tool duringa machining operation.
 2. The cutting tool of claim 1, wherein the firststress relief is circular in cross-sectional shape.
 3. The cutting toolof claim 2, wherein the first stress relief is formed with a radius, R2.4. The cutting tool of claim 1, wherein the first stress relief isformed with a radius, R1.
 5. The cutting tool of claim 1, furthercomprising an axial support surface and a second corner relief betweenthe bottom support surface and the axial support surface.
 6. The cuttingtool of claim 5, further comprising a second stress relief formed in thesecond corner relief, the second stress relief formed at an angle withrespect to a plane parallel to the axial support surface.
 7. The cuttingtool of claim 6, wherein the second stress relief is circular incross-sectional shape.
 8. The cutting tool of claim 6, wherein thesecond stress relief is formed with a radius, R1.
 9. The cutting tool ofclaim 6, wherein the second stress relief is formed with a radius, R3.10. The cutting tool of claim 1, further comprising a third stressrelief formed in the first corner relief at an opposite end of thepocket, the third stress relief formed at an angle with respect to theplane parallel to the radial support surface.
 11. The cutting tool ofclaim 10, wherein the third stress relief is circular in cross-sectionalshape.
 12. The cutting tool of claim 10, wherein the third stress reliefis formed with a radius, R1.
 13. The cutting tool of claim 10, whereinthe third stress relief is formed with a radius, R3.
 14. A cutting toolcomprising: a tool body including a plurality of pockets for receivingcutting inserts, each pocket comprising a bottom support surface, anradial support surface, an axial support surface, a first corner reliefbetween the bottom support surface and the radial support surface, asecond corner relief between the bottom support surface and the axialsupport surface, a first stress relief formed in the first corner reliefat one end of the pocket, the first stress relief formed at an anglewith respect to a plane parallel to the radial support surface, and asecond stress relief formed in the second corner relief at another endof the pocket, the second stress relief formed at an angle with respectto a plane parallel to the axial support surface, wherein the first andsecond stress reliefs reduce a tensile stress of the cutting tool duringa machining operation.
 15. The cutting tool of claim 14, wherein thefirst and second stress reliefs are circular in cross-sectional shape.16. The cutting tool of claim 14, wherein the first stress relief isformed with a radius, R2, and wherein the second stress relief is formedwith a radius, R3.
 17. The cutting tool of claim 14, wherein the firstand second stress reliefs are formed with a radius, R1.
 18. A cuttingtool comprising: a tool body including a plurality of pockets forreceiving cutting inserts, each pocket comprising a bottom supportsurface, an radial support surface, a first corner relief between thebottom support surface and the radial support surface, a first stressrelief formed in the first corner relief at one end of the pocket, thefirst stress relief formed at an angle with respect to a plane parallelto the radial support surface, and a third stress relief formed in thefirst corner relief at an opposite end of the pocket, the third stressrelief formed at an angle with respect to the plane parallel to theradial support surface, wherein the first and third stress reliefsreduce a tensile stress of the cutting tool during a machiningoperation.
 19. The cutting tool of claim 18, wherein the first and thirdstress reliefs are circular in cross-sectional shape.
 20. The cuttingtool of claim 17, wherein the first stress relief is formed with aradius, R2, and wherein the third stress relief is formed with a radius,R3.